Conventional floor steam cleaners comprise a steam head, a steam generator and an integral reservoir. Water from the reservoir flows thought the steam generator and is heated to form steam. Steam is useful in removing oil and sticky matter from a floor. Several methods exist to make the water flow into the reservoir. One method uses a valve to control the water inlet. When the valve is open, gravity causes water to flow into the reservoir. Another method uses a pump to control the flow of water. The above methods have drawbacks such as difficult operation, complex mechanical structure or unstable steam generation.